This invention relates to the field of metal-cutting tools and, more specifically, it relates to those metalcutting tools known as drills.
The prior art method of drilling holes has been by the use of twist drills, twist drills with brazed carbide tips or drills having indexable carbide inserts. The use of drills having indexable carbide inserts is often preferred because of their consistent quality and overall cost effectiveness.
Notwithstanding the economical advantages of drills having indexable carbide inserts, twist drills are still used for holes under about one-half inch in diameter. The principal reason for still using the small twist drills is that it has generally been thought to be impractical to manufacture a small drill having indexable carbide inserts.
It would be desirable to have a small drill that uses indexable carbide inserts because such a tool can drill at higher speeds, for longer periods of time and for less cost than twist drills.
However, the obstacles to manufacturing a small drill having indexable carbide inserts are twofold. Since such drills have a minimum of two inserts, the inserts would have to be made very small so as to both fit on the drill shank. These inserts would be costly to make as well as difficult to handle. The first obstacle then is that a drill employing small indexable carbide inserts simply would not be economical to manufacture. The second obstacle is that the shank would become too weak to withstand the anticipated cutting loads if two inserts were placed on the same end of the shank.
Applicant, however, has solved the problems of the prior art by utilizing a single indexable carbide insert that acts as if it were two inserts. So far as applicant is aware, this is the first use of a single indexable insert on a drill.
A single carbide tip has been used in a ball end mill as shown in U.S. Pat. No. 4,132,493.
It is thus an object of this invention to manufacture a drill that uses indexable carbide inserts and that can drill holes under about one-half inch in diameter.
It is another object of this invention to economically manufacture a drill that uses indexable carbide inserts and that can drill holes under about one-half inch in diameter.
It is a still further object of this invention to manufacture a small drill that uses indexable carbide inserts and that can effectively replace twist drills.